When forming a microprocessor or integrated circuit (commonly referred to as a "chip"), there is provided a metal plate having a plurality of leads formed therein. Thereafter a mass of synthetic resin is molded on the plate in association with the leads so that the leads project therefrom, following which the plate is cut to separate the free ends of the leads therefrom and hence result in the finished chip. Such chip is well known. FIG. 1 illustrates a completed chip having a molded resin mass c and leads a and b projecting therefrom, which leads are normally bent downwardly in parallel relationship. FIG. 2 illustrates the forming of several such chips on a single metal plate L, which plate is conventionally referred to as a "lead frame".
During molding of the resin mass c around the leads a and b when the latter are still fixedly and integrally associated with the lead frame L, the molding process invariably results in the formation of resin burrs or flash at the interface of the metal and resin mass, such as at d. Since this flash or burr is in the vicinity of the leads, it must be removed, and for this purpose removal is oftentimes effected by dry or wet blasting processes. In such processes, the surface of the molded part is blasted and abraded by small particles. Thus, most processes utilize a case for covering critical portions of the lead frame, specifically the molded mass c to prevent blasting and abrasion thereof, whereas other areas of the case are provided with suitable openings so that the blasting material can contact and remove the flash and burrs. However, recent developments with respect to the blasting media have resulted in the development of a new kind of blasting media which can remove the resin burr and flash without abrading the surface of the molded mass c, and hence by use of this blasting media, the lead frame can be subject to the blasting process without requiring use of a protective case.
The handling of the lead frames both before and after the blasting process has been an inefficient and time consuming procedure, often involving substantial manual manipulation. The lead frames are individually and sequentially subjected to the blasting process by means of a known apparatus employing a conveyor which sequentially feeds the lead frames through a blasting chamber, such apparatus being disclosed in Japanese published application No. 53-145965 as owned by the Assignee of this application.
Accordingly, it is an object of this invention to provide an improved process and apparatus for automatically removing resin burrs and flash from the lead frame by use of a blasting process, which process and apparatus permits the continuous and automatic mechanical handling of the lead frame for supply into, through and out of the blasting stage of the apparatus.
More specifically, it is an object of this invention to provide a process and apparatus, as aforesaid, which permits a plurality of lead frames to be supplied to the apparatus within a vertical stack as confined within a holder or cassette. The apparatus includes a loading mechanism which permits the individual lead frames to be supplied sequentially one at a time from a cassette into and through the blasting chamber, and an unloading mechanism which sequentially vertically stacks the lead frames one above the other within another cassette or holder. The holders or cassettes at both the input and output ends of the blasting chamber are preferably mounted on turntables which each hold a plurality of cassettes and which index sequentially to permit emptying or filling of cassettes, whereupon individual lead frames can be sequentially and automatically supplied from the supply turntable to the blasting conveyor for passage through the blasting chamber, and then individually discharged therefrom and transferred into one of the cassettes on the discharge turntable in a sequential and wholly mechanical fashion, thereby permitting a large number of lead frames to be efficiently and rapidly handled wholly mechanically and automatically.
The present invention, in a preferred embodiment, comprises a machine for removing resin burrs or flash from lead frames, which machine permits blasting of the lead frames continuously one after another while permitting the lead frames to be automatically and mechanically supplied from a plurality of cassettes each containing a stack of lead frames therein, with the lead frames after blasting being individually resupplied to and stacked within a plurality of individual cassettes. The machine includes a supply or loading apparatus in the form of a rotatable table having a plurality of cassettes spaced angularly therearound, each cassette being adapted to support a stack of lead frames therein. The table is rotatably indexed such that one of the cassettes is disposed adjacent one end of a conveyor system, whereupon a transfer mechanism sequentially discharges the lower-most lead frame from the cassette onto the upstream end of the conveyor system, which conveyor system then moves the lead frames sequentially through the blasting chamber. A removal or unloading apparatus in the form of a rotatable table having a plurality of angularly spaced cassettes thereon is disposed adjacent the other end of the conveyor system, and a further transfer mechanism sequentially removes the finished lead frames and loads them into one of these latter cassettes.
Other objects and purposes of the invention will be apparent upon reading the following specification and inspecting the accompanying drawings.